Display device

Abstract

The purpose of an embodiment is to provide a display device that achieves an improvement in display quality.　According to one embodiment, a display device comprises: a display module configured to emit display light of linearly polarized light; a first retardation plate facing the display module; a holographic optical element facing the first retardation plate; and a liquid crystal element facing the holographic optical element and configured to reflect first circularly polarized light and transmit second circularly polarized light reverse to the first circularly polarized light. The holographic optical element has a first reflection surface having an inclination angle that increases with increasing distance from a first center intersecting an optical axis, the liquid crystal element has a second reflection surface having an inclination angle that increases with increasing distance from a second center intersecting the optical axis, the inclination angle of the first reflection surface is defined by a quintic odd function of a radius r from the first center, and the inclination angle of the second reflection surface is defined by a quintic odd function of a radius r from the second center.

Description

display device

[0001] FIELD An embodiment of the present invention relates to a display device.

[0002] In recent years, attention has been focused on technology that provides virtual reality (VR) using a head-mounted display worn on a user's head. The head-mounted display is configured to display images on a display placed in front of the user's eyes. This allows a user wearing the head-mounted display to experience a realistic virtual reality space.

[0003] Special Publication No. 2023-510478

[0004] An object of the embodiment is to provide a display device capable of improving display quality.

[0005] According to one embodiment, a display device includes: a display module configured to emit linearly polarized display light; a first retardation plate facing the display module; a holographic optical element facing the first retardation plate; and a liquid crystal element facing the holographic optical element and configured to reflect first circularly polarized light and transmit second circularly polarized light opposite to the first circularly polarized light, wherein the holographic optical element has a first reflective surface whose tilt angle increases with increasing distance from a first center intersecting with an optical axis; the liquid crystal element has a second reflective surface whose tilt angle increases with increasing distance from a second center intersecting with the optical axis; the tilt angle of the first reflective surface is defined by a fifth-order odd function of a radius r from the first center; and the tilt angle of the second reflective surface is defined by a fifth-order odd function of a radius r from the second center.

[0006] According to one embodiment, a display device includes: a display module configured to emit linearly polarized display light; a first retardation plate facing the display module; a holographic optical element facing the first retardation plate; a second retardation plate facing the holographic optical element; and a reflective polarizer facing the second retardation plate, convexly curved toward the holographic optical element, and configured to reflect a first linearly polarized light and transmit a second linearly polarized light orthogonal to the first linearly polarized light; the holographic optical element has a first reflecting surface whose tilt angle increases with increasing distance from a first center intersecting with an optical axis; the reflective polarizer has a curved shape whose tilt angle increases with increasing distance from a third center intersecting with the optical axis; the tilt angle of the first reflecting surface is defined by a fifth-order odd function of a radius r from the first center; and the curved shape is defined by a sixth-order even function of a radius r from the third center.

[0007] FIG. 1 is a perspective view showing an example of the appearance of a head-mounted display 1. FIG. 2 is a cross-sectional view showing an example of the configuration of a display device DSP. FIG. 3 is a cross-sectional view showing an example of the configuration of a liquid crystal element LE. FIG. 4 is a diagram for explaining the optical action of the display device DSP shown in FIG. 2. FIG. 5 is a diagram for explaining the first reflecting surface RS1 and the second reflecting surface RS2. FIG. 6 is a diagram showing simulation results. FIG. 7 is a cross-sectional view showing another example of the configuration of the display device DSP. FIG. 8 is a diagram for explaining an example of the optical action of the display device DSP shown in FIG. 7. FIG. 9 is a diagram for explaining the first reflecting surface RS1 and the curved surface shape. FIG. 10 is a diagram showing simulation results. FIG. 11 is a cross-sectional view showing another example of the configuration of the display device DSP. FIG. 12 is a diagram for explaining the first reflecting surface RS1 and the curved surface shape. FIG. 13 is a diagram showing simulation results.

[0008] The present embodiment will be described below with reference to the drawings. The disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily make while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, the drawings may be schematic in terms of the width, thickness, shape, etc. of each part compared to the actual embodiment for clarity of explanation, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, components that perform the same or similar functions as those described above with reference to the previous drawings are designated by the same reference numerals, and redundant detailed descriptions may be omitted as appropriate.

[0009] In addition, to facilitate understanding, the drawings depict, as necessary, mutually orthogonal X, Y, and Z axes. The direction along the X axis is referred to as the first direction X, the direction along the Y axis is referred to as the second direction Y, and the direction along the Z axis is referred to as the third direction Z. The first direction X and the second direction Y are directions parallel to the substrates that constitute the display device DSP, and the third direction Z corresponds to the thickness direction of the display device DSP. The plane defined by the X and Y axes is referred to as the X-Y plane, and viewing the X-Y plane is referred to as planar view.

[0010] 1 is a perspective view showing an example of the appearance of a head-mounted display 1. The head-mounted display 1 includes, for example, a display device DSPR for the right eye and a display device DSPL for the left eye. When a user wears the head-mounted display 1 on his or her head, the display device DSPR is disposed so as to be located in front of the user's right eye, and the display device DSPL is disposed so as to be located in front of the user's left eye. The display device DSPR has substantially the same configuration as the display device DSPL.

[0011] 2 is a cross-sectional view showing an example of the configuration of the display device DSP. The display device DSP described here can be applied to each of the above-mentioned display devices DSPR and DSPL.

[0012] The display device DSP includes a display module DM and an optical system 4. The display module DM is configured to emit linearly polarized display light DL. The optical system 4 is configured to guide the display light DL from the display module DM to the user's eyes.

[0013] In one example, the display module DM comprises a display panel 2 and an illumination device 3. The display panel 2 is arranged between the illumination device 3 and an optical system 4. The illumination device 3 is arranged on the rear side of the display panel 2 and is configured to illuminate the display panel 2.

[0014] The configuration of the display module DM is not limited to the illustrated example. For example, the display module DM may be a display panel equipped with self-luminous light-emitting elements such as organic electroluminescence (EL) elements, micro LEDs, and mini LEDs. When the display module DM is a display panel equipped with light-emitting elements, the illumination device is omitted.

[0015] The display panel 2 is a transmissive liquid crystal panel formed in a flat plate shape. The display panel 2 includes a first substrate SUB1, a second substrate SUB2, a liquid crystal layer LC, a first polarizer PL1, and a second polarizer PL2. The liquid crystal layer LC is held between the first substrate SUB1 and the second substrate SUB2 in the third direction Z and sealed with a seal SE. The first polarizer PL1 is disposed between the illumination device 3 and the first substrate SUB1 in the third direction Z. The second polarizer PL2 is disposed between the second substrate SUB2 and the optical system 4 in the third direction Z. The surface of the second polarizer PL2 is referred to as a display surface DS. The display surface DS is, for example, parallel to the X-Y plane.

[0016] In the display panel 2, illumination light from the illumination device 3 is selectively modulated by the liquid crystal layer LC, transmitted through the second polarizer PL2, and converted into linearly polarized display light DL.

[0017] The optical system 4 includes a first structure 4A and a second structure 4B. The first structure 4A is spaced apart from the second structure 4B in the third direction Z. An air layer 4C is interposed between the first structure 4A and the second structure 4B. The display panel 2 is disposed between the lighting device 3 and the first structure 4A in the third direction Z. The first structure 4A is disposed between the display panel 2 and the second structure 4B (or between the display panel 2 and the air layer 4C) in the third direction Z.

[0018] The first structure 4A includes a first retardation plate R1 facing the display module DM and a holographic optical element HE facing the first retardation plate R1. In one example, the first retardation plate R1 and the holographic optical element HE are stacked in the third direction Z and bonded to each other.

[0019] The first retardation plate R1 is a quarter-wave plate that imparts a quarter-wave phase difference to the light passing through it. The holographic optical element HE has an interference fringe pattern and a refractive index component with a period corresponding to the wavelength in the thickness direction. Such a holographic optical element HE is configured to reflect and diffract a portion of the incident light in a predetermined direction. The holographic optical element HE has a virtual first reflecting surface (Bragg surface) RS1.

[0020] The second structure 4B includes a liquid crystal element LE facing the holographic optical element HE. The liquid crystal element LE is spaced apart from the holographic optical element HE. An air layer 4C is interposed between the holographic optical element HE and the liquid crystal element LE.

[0021] The liquid crystal element LE includes a liquid crystal layer containing cholesteric liquid crystal, which will be described in detail later. The liquid crystal element LE has a second reflecting surface RS2.

[0022] FIG. 3 is a cross-sectional view showing an example of the configuration of the liquid crystal element LE.

[0023] The liquid crystal element LE includes a substrate 11, an alignment film AL11, a liquid crystal layer LC1, an alignment film AL12, and a substrate 12. The substrates 11 and 12 are transparent substrates that transmit light, and are made of, for example, a transparent glass plate or a transparent synthetic resin plate.

[0024] The alignment film AL11 is disposed on the inner surface of the substrate 11. The alignment film AL12 is disposed on the inner surface of the substrate 12. In the illustrated example, the alignment film AL11 is in contact with the substrate 11, but another thin film may be interposed between the alignment film AL11 and the substrate 11. Similarly, the alignment film AL12 is in contact with the substrate 12, but another thin film may be interposed between the alignment film AL12 and the substrate 12.

[0025] The alignment film AL12 faces the alignment film AL11 in the third direction Z. The alignment films AL11 and AL12 are made of, for example, polyimide, and are both horizontal alignment films that have an alignment regulating force along the XY plane.

[0026] The liquid crystal layer LC1 is disposed between the alignment films AL11 and AL12 and is in contact with the alignment films AL11 and AL12. The liquid crystal layer LC1 has a plurality of liquid crystal structures (cholesteric liquid crystals) LMS. Note that, in Fig. 3, for the sake of simplicity, one liquid crystal molecule LM is shown as a representative liquid crystal molecule that is aligned in the average alignment direction among a plurality of liquid crystal molecules positioned in the X-Y plane.

[0027] Focusing on one liquid crystal structure LMS, the liquid crystal structure LMS has a liquid crystal molecule LM11 located on one end side thereof and a liquid crystal molecule LM12 located on the other end side thereof. The liquid crystal molecule LM11 is adjacent to the alignment film AL11, and the liquid crystal molecule LM12 is adjacent to the alignment film AL12. A plurality of liquid crystal molecules LM including the liquid crystal molecule LM11 and the liquid crystal molecule LM12 are stacked in a spiral shape along the third direction Z while rotating, thereby constituting a cholesteric liquid crystal.

[0028] Furthermore, in the liquid crystal layer LC1, the alignment directions of the plurality of liquid crystal molecules LM11 aligned along the alignment film AL11 and the alignment direction of the plurality of liquid crystal molecules LM12 aligned along the alignment film AL12 change continuously. The illustrated example corresponds to a cross section of the liquid crystal layer LC1 in the X-Z plane, but the cross section of the liquid crystal layer LC1 in the Y-Z plane is similar to the cross section of the liquid crystal layer LC1 in the X-Z plane, and the alignment directions of the plurality of liquid crystal structures LMS adjacent along the second direction Y are different from each other. Note that the alignment direction of the liquid crystal molecules LM here corresponds to the direction of the long axes of the liquid crystal molecules in the X-Y plane.

[0029] The liquid crystal layer LC1 is hardened with the alignment direction of the liquid crystal molecules LM fixed. In other words, the alignment direction of the liquid crystal molecules LM is not controlled in response to an electric field. For this reason, the liquid crystal element LE does not have an electrode for alignment control.

[0030] The liquid crystal layer LC1 has a plurality of second reflecting surfaces RS2, as indicated by dashed lines. The plurality of second reflecting surfaces RS2 reflect some circularly polarized light of the incident light and transmit other circularly polarized light in accordance with Bragg's law. The second reflecting surfaces RS2 here correspond to surfaces on which the liquid crystal molecules LM are aligned or surfaces on which the spatial phases are aligned (equal phase surfaces). The second reflecting surfaces RS2 are curved surfaces that are convex on the side facing the substrate 11 or the side facing the holographic optical element HE shown in FIG. 2 .

[0031] The liquid crystal structure LMS reflects, among light of a specific wavelength λ, circularly polarized light having the same rotation direction as the rotation direction of the cholesteric liquid crystal. For example, if the rotation direction of the cholesteric liquid crystal is clockwise, among light of the specific wavelength λ, right-handed circularly polarized light is reflected and left-handed circularly polarized light is transmitted. Similarly, if the rotation direction of the cholesteric liquid crystal is counterclockwise, among light of the specific wavelength λ, left-handed circularly polarized light is reflected and right-handed circularly polarized light is transmitted.

[0032] FIG. 4 is a diagram for explaining the optical function of the display device DSP shown in FIG.

[0033] First, the display module DM emits display light DL, which is first linearly polarized light LP1, from the display surface DS. Here, the first linearly polarized light LP1 is, for example, linearly polarized light that vibrates in a direction perpendicular to the paper surface. The display light DL passes through the first retardation plate R1 and is converted into first circularly polarized light CP1. Here, the first circularly polarized light CP1 is, for example, left-handed circularly polarized light.

[0034] Of the first circularly polarized light CP1 that has passed through the first phase difference plate R1, a portion of the first circularly polarized light CP1 passes through the holographic optical element HE.

[0035] The first circularly polarized light CP1 transmitted through the holographic optical element HE is reflected by the liquid crystal element LE. In one example, the liquid crystal element LE has a counterclockwise oriented cholesteric liquid crystal and is configured to reflect the first counterclockwise circularly polarized light.

[0036] Of the first circularly polarized light CP1 reflected by the liquid crystal element LE, a portion of the first circularly polarized light CP1 is reflected by the holographic optical element HE. When the first circularly polarized light CP1 is reflected by the holographic optical element HE, the first circularly polarized light CP1 is converted into second circularly polarized light CP2. The second circularly polarized light CP2 is circularly polarized in the opposite direction to the first circularly polarized light CP1, and in this case, for example, is clockwise circularly polarized light.

[0037] The second circularly polarized light CP2 reflected by the holographic optical element HE passes through the liquid crystal element LE and is focused on the pupil E of the user due to the lens action of the holographic optical element HE.

[0038] Note that a portion of the light reflected by the holographic optical element HE and a portion of the light transmitted through the holographic optical element HE are absorbed in the display module DM, and almost none of them reach the pupil E.

[0039] Furthermore, the first linearly polarized light LP1 described with reference to FIG. 4 may be replaced with the second linearly polarized light LP2, and the first circularly polarized light CP1 may be replaced with the second circularly polarized light CP2.

[0040] In such a display device DSP, the optical system 4 has an optical path that passes three times between the holographic optical element HE and the liquid crystal element LE. That is, in the optical system 4, the optical distance between the holographic optical element HE and the liquid crystal element LE is approximately three times the actual distance between the holographic optical element HE and the liquid crystal element LE. As a result, when the display surface DS of the display module DM is treated as an object, the user can observe a magnified virtual image of an object formed at a distance via the optical system 4.

[0041] Next, the first reflecting surface RS1 of the holographic optical element HE and the second reflecting surface RS2 of the liquid crystal element LE will be described in more detail.

[0042] FIG. 5 is a diagram for explaining the first reflecting surface RS1 and the second reflecting surface RS2.

[0043] In Fig. 5, of the normal lines to the display surface DS, the normal line passing through the center Eo of the pupil is defined as the optical axis Op. The optical axis Op is parallel to the third direction Z shown in Fig. 2 and other figures. The point at which the display surface DS intersects with the optical axis Op is referred to as the reference point Rf. The point at which the holographic optical element HE intersects with the optical axis Op is referred to as the first center Ho. The point at which the liquid crystal element LE intersects with the optical axis Op is referred to as the second center Lo.

[0044] Here, the inclination angle of each of the first reflecting surface RS1 and the second reflecting surface RS2 will be explained. Note that the inclination angle in this specification is defined as the angle (acute angle) between the reflecting surface and a plane parallel to the display surface DS (X-Y plane).

[0045] In the holographic optical element HE, the first reflecting surface RS1 is parallel to the display surface DS at the position where it intersects with the optical axis Op, and the tilt angle α1 is zero. The tilt angle α1 increases as it moves away from the first center Ho. The tilt angles α1 of the first reflecting surfaces RS1 located at equal distances from the first center Ho are equal. In this embodiment, the tilt angle α1 is defined as a fifth-order odd function of the radius r from the first center Ho. In other words, the following relational expression (1) holds: α1=A1*r+A3*r ３ +A5*r ５...(1) Here, examples of A1, A3, and A5 are shown in the drawing.

[0046] In the liquid crystal element LE, the second reflecting surface RS2 is parallel to the display surface DS at the position where it intersects with the optical axis Op, and the inclination angle α2 is zero. The inclination angle α2 increases as it moves away from the second center Lo. The inclination angles α2 of the second reflecting surfaces RS2 positioned at equal distances from the second center Lo are equal. In this embodiment, the inclination angle α2 is defined as a fifth-order odd function of the radius r from the second center Lo. In other words, the following relational expression (2) holds: α2=C1*r+C3*r ３ +C5*r ５ ...(2) Here, examples of C1, C3, and C5 are shown in the drawing.

[0047] The figure shows one of the principal rays PB that reach the center Eo of the pupil out of the light emitted from the display surface DS of the display module DM. The angle between the optical axis Op and the principal ray PB is defined as θ.

[0048] Here, a plane (for example, the XZ plane) that includes the optical axis Op and the principal ray PB is called a meridian plane, and a plane that is perpendicular to the meridian plane and that includes the principal ray PB is called a sagittal plane.

[0049] Next, the inventors performed a simulation using ray tracing to calculate the transverse aberration Δφx in the meridional plane and the transverse aberration Δφy in the sagittal plane. Generally, the transverse aberration is defined by the distances Δx and Δy on the image plane, but here it is defined by the angles Δφx and Δφy at which Δx and Δy are viewed from the center of the pupil, respectively.

[0050] FIG. 6 is a diagram showing the simulation results.

[0051] Simulations were performed for angles θ between the optical axis Op and the chief ray PB of 0°, 10°, 20°, 30°, 40°, and 50°, and the results are shown in graphs. In each graph, the horizontal axis represents the distances xp (mm) and yp (mm) from the center of the pupil to the point where each ray passes through the pupil plane, and the vertical axis represents the transverse aberrations Δφx and Δφy (arc-min).

[0052] In this simulation, the inclination angle α1 of the first reflecting surface RS1 is defined by the above-mentioned relational expression (1), and the values ​​of A1, A3, and A5 are the values ​​shown in Fig. 5. The inclination angle α2 of the second reflecting surface RS2 is defined by the above-mentioned relational expression (2), and the values ​​of C1, C3, and C5 are the values ​​shown in Fig. 5.

[0053] According to the simulation results shown in the figure, assuming a pupil diameter of 3 mm, it was confirmed that all lateral aberrations were within ±1 when the distances xp and yp were in the range of −1.5 mm to +1.5 mm.

[0054] As described above, according to this embodiment, in the optical system 4 of the display device DSP, the tilt angle of the first reflecting surface RS1 included in the holographic optical element HE and the tilt angle of the second reflecting surface RS2 included in the liquid crystal element LE are optimized, thereby mitigating the effects of aberration, and thus improving the display quality.

[0055] The inventors also conducted a separate simulation for a comparative example. In this comparative example, the holographic optical element HE has a retroreflective surface, and an optical system equipped with a flat reflective polarizing plate instead of a liquid crystal element is used. Simulations of this comparative example confirmed that the transverse aberration Δφx in the meridional plane increases with increasing angle θ. In particular, when the angle θ exceeds 10°, the transverse aberration Δφx exceeds 2 when the distance xp exceeds ±1 mm. On the other hand, the transverse aberration Δφy in the sagittal plane is approximately within ±1 regardless of the angle θ. Thus, in the comparative example, it was confirmed that the transverse aberration Δφx increases with increasing angle θ.

[0056] Next, another configuration example will be described.

[0057] 7 is a cross-sectional view showing another example of the configuration of the display device DSP. The display device DSP described here can be applied to each of the display devices DSPR and DSPL shown in FIG.

[0058] The configuration example shown in Fig. 7 differs from the configuration example shown in Fig. 2 in the optical system 4. The main differences will be described below. Note that the display module DM is the same as the configuration example shown in Fig. 2 and detailed description will be omitted, but it is configured to emit linearly polarized display light DL.

[0059] The optical system 4 includes a first structure 4A and a second structure 4B. The first structure 4A is spaced apart from the second structure 4B in the third direction Z. An air layer 4C is interposed between the first structure 4A and the second structure 4B.

[0060] The first structure 4A includes a first retardation plate R1 facing the display module DM, a holographic optical element HE facing the first retardation plate R1, and a second retardation plate R2 facing the holographic optical element HE. In one example, the first retardation plate R1, the holographic optical element HE, and the second retardation plate R2 are stacked in the third direction Z and bonded to one another.

[0061] The first retardation plate R1 and the second retardation plate R2 are quarter-wave plates that impart a phase difference of a quarter wavelength to the light passing through them. The holographic optical element HE has a virtual first reflecting surface (Bragg surface) RS1, similar to the configuration example shown in FIG.

[0062] The second structure 4B includes a reflective polarizer PR facing the second retardation plate R2. The reflective polarizer PR is spaced apart from the second retardation plate R2. An air layer 4C is interposed between the second retardation plate R2 and the reflective polarizer PR.

[0063] The reflective polarizer PR is curved convexly toward the holographic optical element HE and is configured to reflect a first linearly polarized light component of the incident light and transmit a second linearly polarized light component that is orthogonal to the first linearly polarized light component.

[0064] FIG. 8 is a diagram for explaining an example of the optical action of the display device DSP shown in FIG.

[0065] First, the display module DM emits display light DL, which is first linearly polarized light LP1, from the display surface DS. The display light DL passes through the first retardation plate R1 and is converted into first circularly polarized light CP1.

[0066] Of the first circularly polarized light CP1 that has passed through the first retardation plate R1, a portion of the first circularly polarized light CP1 passes through the holographic optical element HE. The first circularly polarized light CP1 that has passed through the holographic optical element HE passes through the second retardation plate R2 and is converted into first linearly polarized light LP1.

[0067] The first linearly polarized light LP1 that has passed through the second retardation plate R2 is reflected by the reflective polarizer PR. The first linearly polarized light LP1 that has been reflected by the reflective polarizer PR is then passed through the second retardation plate R2 and converted into the first circularly polarized light CP1.

[0068] Of the first circularly polarized light CP1 that has passed through the second retardation plate R2, a portion of the first circularly polarized light CP1 is reflected by the holographic optical element HE. When the first circularly polarized light CP1 is reflected by the holographic optical element HE, the first circularly polarized light CP1 is converted into second circularly polarized light CP2.

[0069] The second circularly polarized light CP2 reflected by the holographic optical element HE passes through the second phase difference plate R2 and is converted into second linearly polarized light LP2.

[0070] The second linearly polarized light LP2 transmitted through the second retardation plate R2 is transmitted through the reflective polarizer PR and is focused on the pupil E of the user through the lens action of the holographic optical element HE and the curved reflective polarizer PR.

[0071] Note that a portion of the light reflected by the holographic optical element HE and a portion of the light transmitted through the holographic optical element HE are absorbed in the display module DM, and almost none of them reach the pupil E.

[0072] Furthermore, the first linearly polarized light LP1 described with reference to FIG. 8 may be replaced with the second linearly polarized light LP2, and the first circularly polarized light CP1 may be replaced with the second circularly polarized light CP2.

[0073] Next, the curved surface shapes of the first reflecting surface RS1 of the holographic optical element HE and the reflective polarizing plate PR will be described in more detail.

[0074] FIG. 9 is a diagram for explaining the first reflecting surface RS1 and the curved surface shape.

[0075] 9, of the normal lines to the display surface DS, the normal line passing through the center Eo of the pupil is defined as the optical axis Op. The optical axis Op is parallel to the third direction Z shown in FIG. 2 and other figures. The point at which the display surface DS intersects with the optical axis Op is referred to as the reference point Rf. The point at which the holographic optical element HE intersects with the optical axis Op is referred to as the first center Ho. The point at which the reflective polarizing plate PR intersects with the optical axis Op is referred to as the third center Po.

[0076] Here, the inclination angle and curved surface shape of the first reflecting surface RS1 will be described.

[0077] In the holographic optical element HE, the first reflecting surface RS1 is parallel to the display surface DS at the position where it intersects with the optical axis Op, and the tilt angle α1 is zero. The tilt angle α1 increases as it moves away from the first center Ho. The tilt angles α1 of the first reflecting surfaces RS1 located at equal distances from the first center Ho are equal. In this embodiment, the tilt angle α1 is defined as a fifth-order odd function of the radius r from the first center Ho. In other words, the following relational expression (1) holds: α1=A1*r+A3*r ３ +A5*r ５ ...(1) Here, examples of A1, A3, and A5 are shown in the drawing.

[0078] In the reflective polarizing plate PR, the inclination angle of the curved surface shape is defined as the angle (acute angle) formed between the tangent to the curved reflective polarizing plate PR and a plane (X-Y plane) parallel to the display surface DS. The inclination angle of the curved surface shape increases as it moves away from the third center Po. The inclination angle is the same at positions equidistant from the third center Po. In this embodiment, the curved surface shape S is defined as a sixth-order even function of the radius r from the third center Po. In other words, the following relational expression (3) holds: S=T+C2*r ２ +C4*r ４ +C6*r ６...(3) where T is the distance along the optical axis Op from the reference point rf to the third center Po, and examples of C2, C4, and C6 are shown in the drawing.

[0079] The figure shows one of the principal rays PB that reach the center Eo of the pupil out of the light emitted from the display surface DS of the display module DM. The angle between the optical axis Op and the principal ray PB is defined as θ.

[0080] Next, the inventors performed a simulation using a ray tracing method to calculate the transverse aberration Δφx in the meridional plane and the transverse aberration Δφy in the sagittal plane.

[0081] FIG. 10 is a diagram showing the simulation results.

[0082] Simulations were performed for angles θ between the optical axis Op and the chief ray PB of 0°, 10°, 20°, 30°, 40°, and 50°, and the results are shown in graphs. In each graph, the horizontal axis represents the distances xp (mm) and yp (mm) from the center of the pupil to the point where each ray passes through the pupil plane, and the vertical axis represents the transverse aberrations Δφx and Δφy (arc-min).

[0083] In this simulation, the inclination angle α1 of the first reflecting surface RS1 is defined by the above relational expression (1), and the values ​​applied to A1, A3, and A5 are the values ​​shown in Fig. 9. The curved surface shape S is defined by the above relational expression (3), and the values ​​applied to C2, C4, and C6 are the values ​​shown in Fig. 9, and T is 9 mm.

[0084] According to the simulation results shown in the figure, assuming a pupil diameter of 3 mm, it was confirmed that all lateral aberrations were within ±1 when the distances xp and yp were in the range of −1.5 mm to +1.5 mm.

[0085] As described above, according to this embodiment, in the optical system 4 of the display device DSP, the tilt angle of the first reflecting surface RS1 included in the holographic optical element HE and the curved surface shape of the curved reflective polarizing plate PR are optimized, thereby mitigating the effects of aberration and improving the display quality.

[0086] 11 is a cross-sectional view showing another example of the configuration of the display device DSP. The display device DSP described here can be applied to each of the display devices DSPR and DSPL shown in FIG.

[0087] The configuration example shown in Fig. 11 differs from the configuration example shown in Fig. 7 in the optical system 4. The main differences will be described below. Note that the display module DM is the same as the configuration example shown in Fig. 2 and detailed description will be omitted, but it is configured to emit linearly polarized display light DL.

[0088] The optical system 4 includes a first structure 4A and a second structure 4B. The first structure 4A is spaced apart from the second structure 4B in the third direction Z. An air layer 4C is interposed between the first structure 4A and the second structure 4B.

[0089] The first structure 4A includes a first retardation plate R1 facing the display module DM, a holographic optical element HE facing the first retardation plate R1, and a second retardation plate R2 facing the holographic optical element HE.

[0090] The second structure 4B includes a reflective polarizer PR facing the second retarder R2 and a lens element LS facing the reflective polarizer PR. The lens element LS is a plano-convex lens having a convex surface LSA in contact with the reflective polarizer PR and a flat surface LSB on the opposite side of the convex surface LSA. In one example, the reflective polarizer PR and the lens element LS are stacked in the third direction Z and bonded to each other. The reflective polarizer PR arranged on the convex surface LSA is curved convexly toward the holographic optical element HE. By being bonded to the convex surface LSA, the reflective polarizer PR is more likely to maintain its shape.

[0091] The optical action of the display device DSP having such a configuration example is substantially the same as that of the example shown in FIG. 8, and therefore a description thereof will be omitted.

[0092] Next, the curved surface shapes of the first reflecting surface RS1 of the holographic optical element HE and the reflective polarizing plate PR will be described in more detail.

[0093] FIG. 12 is a diagram illustrating the first reflecting surface RS1 and the curved surface shape.

[0094] In the holographic optical element HE, the tilt angle α1 of the first reflecting surface RS1 is defined as a fifth-order odd function of the radius r from the first center Ho. That is, the following relational expression (1) holds: α1=A1*r+A3*r ３ +A5*r ５ ...(1) Here, examples of A1, A3, and A5 are shown in the drawing.

[0095] The curved surface shape of the reflective polarizing plate PR depends on the shape of the convex surface LSA of the lens element LS. The curved surface shape S is defined by a sixth-order even function of the radius r from the third center Po. In other words, the following relational expression (3) holds: S=T+C2*r ２ +C4*r ４ +C6*r ６ ...(3) where T is the distance along the optical axis Op from the reference point rf to the third center Po, and examples of C2, C4, and C6 are shown in the drawing.

[0096] Next, the inventors performed a simulation using a ray tracing method to calculate the transverse aberration Δφx in the meridional plane and the transverse aberration Δφy in the sagittal plane.

[0097] FIG. 13 is a diagram showing the simulation results.

[0098] Simulations were performed for angles θ between the optical axis Op and the chief ray PB of 0°, 10°, 20°, 30°, 40°, and 50°, and the results are shown in graphs. In each graph, the horizontal axis represents the distances xp (mm) and yp (mm) from the center of the pupil to the point where each ray passes through the pupil plane, and the vertical axis represents the transverse aberrations Δφx and Δφy (arc-min).

[0099] In this simulation, the inclination angle α1 of the first reflecting surface RS1 is defined by the above relational expression (1), and the values ​​shown in Figure 12 are applied to A1, A3, and A5. The curved surface shape S is defined by the above relational expression (3), and the values ​​shown in Figure 12 are applied to C2, C4, and C6, and T is 9 mm. The lens element LS is made of glass with a refractive index of 1.5 and has a thickness of 1.9 mm on the optical axis.

[0100] According to the simulation results shown in the figure, assuming a pupil diameter of 3 mm, it was confirmed that all lateral aberrations were within ±1 when the distances xp and yp were in the range of −1.5 mm to +1.5 mm.

[0101] As described above, according to this embodiment, in the optical system 4 of the display device DSP, the tilt angle of the first reflecting surface RS1 included in the holographic optical element HE and the curved surface shape of the curved reflective polarizing plate PR are optimized, thereby mitigating the effects of aberration and improving the display quality.

[0102] In each of the above configuration examples, various anti-reflection layers may be applied in order to suppress undesired reflection on the surface of the optical element.

[0103] As described above, according to this embodiment, it is possible to provide a display device capable of improving display quality.

[0104] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as defined in the claims.

[0105] REFERENCE SIGNS LIST 1...head mounted display DSP...display device DM...display module 4...optical system HE...holographic optical element RS1...first reflecting surface LE...liquid crystal element RS2...second reflecting surface LMS...liquid crystal structure (cholesteric liquid crystal) PR...reflective polarizer LS...lens element R1...first retardation plate R2...second retardation plate

Claims

1. A display device comprising: a display module configured to emit linearly polarized display light; a first retardation plate facing said display module; a holographic optical element facing said first retardation plate; and a liquid crystal element facing said holographic optical element and configured to reflect first circularly polarized light and transmit second circularly polarized light opposite to the first circularly polarized light, wherein said holographic optical element has a first reflecting surface whose tilt angle increases with increasing distance from a first center intersecting with an optical axis; and said liquid crystal element has a second reflecting surface whose tilt angle increases with increasing distance from a second center intersecting with the optical axis, wherein the tilt angle of said first reflecting surface is defined by a fifth-order odd function of a radius r from said first center; and wherein the tilt angle of said second reflecting surface is defined by a fifth-order odd function of a radius r from said second center.

2. The display device according to claim 1, wherein the first retardation plate and the holographic optical element are in contact with each other, and the liquid crystal element is spaced apart from the holographic optical element.

3. The display device according to claim 1, wherein the liquid crystal element includes a liquid crystal layer containing cholesteric liquid crystal and cured with the orientation direction of a plurality of liquid crystal molecules fixed, and the second reflecting surface is formed as an equiphase surface in which the orientation directions of the liquid crystal molecules are aligned.

4. The display device according to claim 1, wherein the first retardation plate is a quarter-wave plate.

5. A display device comprising: a display module configured to emit linearly polarized display light; a first retardation plate facing said display module; a holographic optical element facing said first retardation plate; a second retardation plate facing said holographic optical element; and a reflective polarizer facing said second retardation plate, convexly curved toward said holographic optical element, and configured to reflect a first linearly polarized light and transmit a second linearly polarized light orthogonal to the first linearly polarized light; wherein said holographic optical element has a first reflecting surface whose tilt angle increases with increasing distance from a first center intersecting with an optical axis; and said reflective polarizer has a curved shape whose tilt angle increases with increasing distance from a third center intersecting with the optical axis; the tilt angle of said first reflecting surface is defined by a fifth-order odd function of radius r from said first center; and said curved shape is defined by a sixth-order even function of radius r from said third center.

6. The display device according to claim 5, wherein the first retardation plate, the holographic optical element, and the second retardation plate are stacked, and the reflective polarizer is spaced apart from the second retardation plate.

7. The display device according to claim 5, further comprising a lens element having a convex surface in contact with said reflective polarizing plate and a flat surface opposite said convex surface.

8. The display device according to claim 5, wherein the first retardation plate and the second retardation plate are quarter-wave plates.

Images